Morphing structures for aircraft

Tiny identical interlocking composite fiber loops create airplane wings that behave like an elastic solid and are ten times stiffer per weight than other ultralight materials.

MIT researchers have developed a lightweight structure whose tiny blocks can be snapped together much like the bricks of a child's construction toy. The new material, the researchers say, could revolutionize the assembly of airplanes, spacecraft, and even larger structures, such as dikes and levees.

... this new structure can also be disassembled and reassembled easily -- such as to repair damage, or to recycle the parts into a different configuration.

The individual parts can be mass-produced; Gershenfeld and Cheung are developing a robotic system to assemble them into wings, airplane fuselages, bridges or rockets -- among many other possibilities.

The new design combines three fields of research, Gershenfeld says: fiber composites, cellular materials (those made with porous cells) and additive manufacturing (such as 3-D printing, where structures are built by depositing rather than removing material).

The system is useful for "anything you need to move, or put in the air or in space,"...... these new structures are made by linking many small composite fiber loops, Cheung and Gershenfeld show that they behave like an elastic solid, with a stiffness, or modulus, equal to that of much heavier traditional structures -- because forces are conveyed through the structures inside the pieces and distributed across the lattice structure.

What's more, when conventional composite materials are stressed to the breaking point, they tend to fail abruptly and at large scale. But the new modular system tends to fail only incrementally, meaning it is more reliable and can more easily be repaired, the researchers say. "It's a massively redundant system," Gershenfeld says.

The researchers show that by combining different part types, they can make morphing structures with identical geometry but that bend in different ways in response to loads: Instead of moving only at fixed joints, the entire arm of a robot or wing of an airplane could change shape.

... this new approach to building structures "is really disruptive. It opens interesting opportunities in the way to design and manufacture aerostructures." [emphasis mine]

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Fascinating report. Even primitive builders understood the extra strength produced by circles, squares, and triangles and now these researchers look to cellular structures for design of materials.

"Cheung produced flat, cross-shaped composite pieces that were clipped into a cubic lattice of octahedral cells, a structure called a "cuboct" -- which is similar to the crystal structure of the mineral perovskite, a major component of Earth's crust."

"Each of the bricks is fashioned out of carbon fiber impregnated with epoxy resin, formed into the shape of a flat X. Each X has a hole in the middle, which the leg of another X slots into (pictured above). The end result is a very stiff structure of vertex-connected octahedrons, or, as the researchers call them, “cubocts.” These cubocts can be added, removed, and reoriented to build different structures with different strengths (one might be resistant to crushing, while one might be difficult to twist). To put it into numbers, structures made out of these bricks are capable of withstanding 12.3 megapascals of compressive force (pressure), with a very low density of 7.2 milligrams per cubic centimeter. MIT says this is 10 times stiffer than other materials of the same density.?